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Peter lake lies deep in a maple forest near the wisconsin-michigan border. One day in July 2008 a group of scientists and graduate students led by ecologist Stephen Carpenter of the University of Wisconsin–Madison arrived at the lake with some fish. One by one, they dropped 12 largemouth bass into the water. Then they headed for home, leaving behind sensors that could measure water clarity every five minutes, 24 hours a day.

The scientists repeated the same trip two more times in 2009. Each time they dropped 15 more bass into the water. Months passed. The lake cycled through the seasons. It froze over, thawed out and bloomed again with life. Then, in the summer of 2010, Peter Lake changed dramatically. Before the scientists started their experiment, the lake abounded in fathead minnows, pumpkinseeds and other small fish. Now, however, those once dominant predators were rare, for the most part eaten by the largemouth bass. The few survivors hid in the shallows. Water fleas and other tiny animals that the small fish once devoured were now free to flourish. And because these diminutive animals graze on algae, the lake water became clearer. Two years later the ecosystem remains in its altered state.